Metal substrates, including but not limited to various manufacture components and/or parts, are often treated with an electro-deposition coating prior to final finishing, e.g., painting. The substrate must be clean prior to application of the electro-deposition coating. Typically, and particularly in mass production, the substrate is cleaned in a wet cleaning process with a water based solvent, such as but not limited to an acid solvent or a base solvent. The substrate is allowed to dry and then submerged in a bath of the electro-deposition solution, whereupon an electrical charge is applied to the metal substrate, which attracts oppositely charged paint particles suspended in a water based solution. The electro-deposition coating process provides a protective film over the entire surface of the substrate.
An “electroless” electro-deposition coating process has been developed for coating a substrate manufactured from and/or including a magnesium alloy with the electro-deposition solution. The electroless coating process applies the electro-deposition solution to the magnesium alloy substrate without applying the electrical charge to the magnesium alloy substrate. Accordingly, the electroless coating process does not require an electrical charge. Rather, the electroless coating process submerges the substrate in the bath of the electro-deposition solution, or a solution similar to the electro-deposition solution, to apply the electro-deposition solution such that a layer of polymer containing materials are deposited onto the magnesium alloy substrate due to a surface alkalization effect.
The electroless coating process is less effective when applied to a magnesium alloy substrate having a magnesium hydroxide layer on the outer surface of the substrate. Because the reaction between the magnesium alloy substrate and the wet cleaning solution produces a magnesium hydroxide layer on the outer surface of the substrate, the magnesium alloy substrate may be “dry polished”, i.e., cleaned in the absence of a water based solution, so as to form a magnesium oxide layer on the outer surface of the substrate instead of the magnesium hydroxide layer formed when using the wet cleaning solution. The electroless coating process is more effective when applied to a fresh magnesium alloy substrate without any surface films, or on a magnesium alloy substrate having a magnesium oxide layer on the outer surface of the substrate.